Possibility of replay attacks in manually keyed IPsec?

[Mikael Olsson <mikael.olsson () enternet se>]

Hello,

Quick question. I'm getting conflicting answers from different 
people, so I decided I'd hand it over to you guys:

Is IPsec vulnerable to replay attacks when IKE is configured
to use pre-shared keys, rather than basing the SA negotiation 
on certificates?

I'd imagine that if IPsec itself uses fixed encryption keys,
it would be vulnerable to replay attacks, but this is not
the case. Here, we only handle fixed keys to IKE, so the
fixed keys only get used in the SA negotiation.

(If there is a vulnerability, is this a flaw in the algorithm, 
or just in someone's imlementation of it?)

Thanks in advance,
/Mike

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Mikael Olsson, EnterNet Sweden AB, Box 393, S-891 28 ÖRNSKÖLDSVIK
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